HP HP12C hp 12c_user's guide_English_E_HDPMBF12E44.pdf - Page 79

Section 6: Statistics Functions 79 Standard Deviation Pressing gv calculates the standard deviation of the x-values (sx) and of the y-values (sy). (The standard deviation of a set of data is a measure of the dispersion around the mean.) The standard deviation of the x-values appears in the display after v is pressed; to display the standard deviation of the y-values, press ~. Example: To calculate the standard deviations of the x-values and of the y-values from the preceding example: Keystrokes gv ~ Display 4,820.59 6.03 Standard deviation of sales. Standard deviation of hours worked. The formulas used in the hp 12c for calculating sx, and sy give best estimates of the population standard deviation based on a sample of the population. Thus, current statistical convention calls them sample standard deviations. So we have assumed that the seven salespersons are a sample of the population of all salespersons, and our formulas derive best estimates of the population from the sample. What if the seven salespersons constituted the whole population of salespersons. Then we wouldn't need to estimate the population standard deviation. We can find the true population standard deviation (σ) when the data set equals the total population, using the following keystrokes.* Keystrokes gÖ _ gv ~ Display 21,714.29 8.00 4,463.00 5.58 Mean (dollars) Number of entries + 1. σx σy To continue summing data pairs, press gÖg^ before entering more data. * It turns out that if you sum the mean of the population into the set itself and find the new s, computed using the formulas on page 192, that s will be the population standard deviation, σ, of the original set. File name: hp 12c_user's guide_English_HDPMBF12E44 Printered Date: 2005/7/29 Page: 79 of 209 Dimension: 14.8 cm x 21 cm